I think it is best to experiment with cheap sails. The shortcoming when changing cloth is that elasticity changes, so the cut would be different. But they will give you a good idea of drive and heeling force. Recutting old sails can be a good source, also used windsurfer sails.
I like low aspect traditional rigs like lug rigs. They give good drive for less heel, and work well with shorter spars. This makes them easier to rig, and easier to store. There are some good examples of these on the yahoo forum, and also on the woodenboat forum.
As far as reefing, you might consider different rigs for heavy or light air. I think if I got caught in a canoe or kayak with too much sail, I'd take it all in and paddle. You can use a downhaul on a marconi rig, or a lug rig's yard will brnig it down. I agree that sock type sails, and even sprit rigs, can be dangerous because they won't come down on deck. I think you'll be surprised how easily driven a kayak is by small amounts of sail. Remember you don't develope much force with a paddle, way less than 1 hp I'm sure.